This invention relates to a transconductor-capacitor integrator for generating at least one output signal which is proportional to the integral of an input signal, which integrator comprises an input terminal for receiving the input signal, an output terminal for supplying the output signal, a capacitor and, coupled thereto, a transconductor having an input and an output.
Such a transconductor-C integrator is known, inter alia, from the article "A 4-MHz CMOS Continuous-Timer Filter with On-Chip Automatic Tuning", IEEE Journal of Solid State Circuits, Vol. 23, No. 3, June 1988, pp. 750-758, FIG. 1. Continuous-time filters are suitable for a variety of filter functions in the field of audio and video signal processing and as anti-alias filters in digital or switched-capacitor systems. Continuous-time filters require a transconductor-C integrator with a linear tunable transconductor. However, tuning capability and linearity cannot be combined simply. In addition, there is a need for transconductor-C integrators operating in the current mode, i.e. the input and the output signals take the form of currents. This need is fostered by the trend towards lower supply voltages and the search for improved high-frequency performance of the filter systems. The advantages of the current mode over the voltage mode have been mentioned, inter alia, in the article "All current-mode frequency selective circuits", Electronics Letters, Jun. 8, 1989, Vol. 25, No. 12, pp. 759-761.